The 5-member user group has requested funds for a JEOL-100CX electron microscope (100KV) because the present EM facilities available to this group are not adequate for their ultrastructural studies. Reasons for this request include very heavy user demand on the two microscopes available to the user group (Philips 200 and Philips 300) and the poor service reliability and technical limitations of these two instruments. The research activities of the user group which require use of the EM fall into six main areas of investigation. These include (a) analysis of cytoskeletal structure and motility in nonmuscle cells, (b) characterization of nerve and muscle mutants in Drosophila, (c) analysis of nerve growth and synapse formation in regenerating neurons of Lamprey, (d) characterization of uptake of exogenously added DNA by mammalian tissue culture cells. All of the above studies will require standard thinsection techniques. In addition, studies will require a goniometer stage to produce stereo images of whole-mount tissue culture cells, deep-etch replicas made using quick-freeze techniques, and microvillar filament bundles in negatively stained preparations.